Matt 12:3 He said to them, “Have you not read what David did when he and his companions were hungry, how he went into the house of God and ate the bread of offering, which neither he nor his companions but only the priests could lawfully eat? Or have you not read in the law that on the Sabbath the priests serving in the temple violate the Sabbath and are innocent? (See 1 Sam 21:2-7.)
The Question in Context:
Our Lord asks us this question: “Have you not read…?” Specifically, in this passage, He is responding to a criticism the Pharisees level at the disciples for picking heads of grain on the Sabbath, from a field they were walking through and eating the grains.
Our Lord’s encyclopedic knowledge of Scripture leaps out at the Pharisees and silences them…and then challenges them to four additional passages to explain the actions of His disciples, ending with “For the Son of Man is Lord of the Sabbath (Matt 12:8).” They become furious at Him, but more on that in the next question. At the end of this passage, Christ essentially makes Himself out to be equal to God.
Know Jesus, Know Scripture – No Jesus, No Scripture
Back to the question, then. “Have you not read…?” This is a call for us to get into God’s Word: Old Testament and New Testament. Jesus wants us to have knowledge of the thoughts of God and the stories of His people. Back in Matt 10:26, Jesus tells us “Therefore do not be afraid of them. Nothing is concealed that will not be revealed, nor secret that will not be known.”
Taken in context here, when we know Scripture, we know Jesus. Just ask St. Jerome (“Ignorance of Scripture is ignorance of Christ.”)! When we read Holy 
Scripture, we do more than spit out laws, as the Pharisees do in this passage. Rather, we know we are acting within God’s mercy. We know that the Sabbath was made for us, not the other way around. And we know that when we follow Christ as His disciples, He will let us feed readily, both on the grain of the Bread of Life, but also on the meal of His Holy Word.